1. Field of the Invention
This invention relates to a thin magnetic element comprising a coil pattern formed on a substrate and a thin magnetic film formed on the coil pattern; and a transformer equipped with the element.
2. Description of the Related Art
Reflecting the size reduction and performance improvement of a magnetic element, a soft magnetic material is required to have a high magnetic permeability at a frequency not lower than several hundreds MHz, particularly, to have a high saturation magnetic flux density of 5 kG or higher and at the same, high specific resistance and low coercive force. In a transducer, among various applications, a soft magnetic material having a high specific resistance is especially requested.
As magnetic materials having a high saturation magnetic flux density, Fe and a number of and alloys composed mainly of Fe are known. When manufactured using such an alloy by the film forming technique such as sputtering method, the thin magnetic film so obtained has a high coercive force and small specific resistance in spite of a high saturation magnetic flux density and it is difficult to obtain good soft magnetic properties in a high frequency region. In addition, ferrite frequently employed as a bulk material does not provide excellent soft magnetic properties when formed into a thin film.
As one of the causes for the reduction of a magnetic permeability at high frequency is a loss caused by the generation of an eddy current. For the prevention of such an eddy current loss which is one of the causes for the reduction the magnetic permeability at high frequency, there is accordingly a demand for a reduction in the film thickness and an increase in the resistance of a thin film.
It is however very difficult to heighten the specific resistance while maintaining the magnetic properties. A soft thin magnetic film formed of a crystal alloy, for example, Sendust or an amorphous alloy has a specific resistance as small as several tens xcexcQxc2x7cm. There is accordingly a demand for soft magnetic alloys having an increased specific resistance with a saturation magnetic flux density being maintained at 5 kG (0.5 T) or greater.
When a soft magnetic alloy is formed into a thin film, it becomes more difficult to obtain good soft magnetic properties owing to an influence of the generation of magneto striction, or the like.
Particularly in the case where a thin magnetic element is formed by disposing a thin film of a soft magnetic alloy close to a coil, it is still more difficult to obtain a high inductance and figure of merit while maintaining good soft magnetic properties which the soft magnetic alloy originally has possessed and also to control a temperature rise during use. In the conventional thin magnetic element of such a type, a loss increase occurs in the thin film formed of a soft magnetic alloy prior to the lowering in the figure of merit Q of a coil itself constituting a magnetic core, resulting in the tendency to limit the high-frequency properties which a transducer or reactor should have as a thin magnetic film. In other words, the application, as a thin magnetic film, of a Co-group amorphous thin film, a Ni-Fe alloy thin film or the like which has excellent soft magnetic properties can be considered but such a thin film does not have a high specific resistance and is apt to increase a loss at high frequency, whereby the high-frequency properties of the entire magnetic element tend to be limited.
With the forgoing in view, the present invention has been completed. An object of the present invention is to provide a thin magnetic element which can be reduced in its thickness, exhibits a high inductance and figure of merit Q, can meet the use at a high frequency region and does not emit heat so much; and also to provide a transformer equipped with the thin magnetic element.
With a view to overcoming the above-described problems, the present invention provides a thin magnetic element which comprises a coil pattern formed on one side or both sides of a substrate and a thin magnetic film formed on said coil pattern, said thin magnetic film being formed to a thickness of 0.5 xcexcm or greater but 8 xcexcm or smaller; and at least one of the following conditions is satisfied: assuming that the thickness and width of a coil conductor constituting a coil pattern are xe2x80x9ctxe2x80x9d and xe2x80x9caxe2x80x9d, respectively, an aspect ratio t/a of the coil conductor satisfies the relationship of 0.035xe2x89xa6t/axe2x89xa60.35; and assuming that the width of the coil conductor constituting the coil pattern is a and the distance between the mutually adjacent coil conductors in the coil pattern is b, the relationship of 0.2xe2x89xa6a/(a+b) is satisfied.
A good figure of merit Q can be attained by forming the thin magnetic film on the coil pattern to the above-described thickness; a temperature rise of the coil conductor can be suppressed by setting the aspect ratio of the coil conductor within the above-described range; and a stably high inductance, low equivalent resistance and good figure of merit Q can be achieved by satisfying the relationship of 0.2xe2x89xa6a/(a+b).
In the above-described constitution, it is preferred that the thin magnetic film comprises a fine crystalline phase having an average grain size of 30 nm or smaller and being composed mainly of at least one element selected from the group consisting of Fe, Co and Ni, and an amorphous phase composed mainly of a compound consisting of at least one element M selected from the group consisting of lanthanoide type rare earth elements (at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu), Ti, Zr, Hf, Ta, Nb, Mo and W, and O or N.
It is more preferred that the above-described thin magnetic film has a composition represented by the following composition formula:
AaMbMxe2x80x2cLd
wherein A represents at least one element selected from the group consisting of Fe, Co and Ni, M represents at least one element selected from the group consisting of lanthanoide type rare earth elements (at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu) and Ti, Zr, Hf, V, Nb, Ta and W, Mxe2x80x2 represents at least one element selected from the group consisting of Al, Si, Cr, Pt, Ru, Rh, Pd and Ir; L represents at least one of the elements O and N; and a, b, c and d represent compounding ratios satisfying the relationships of 20xe2x89xa6a xe2x89xa685, 5xe2x89xa6b xe2x89xa630, 0xe2x89xa6cxe2x89xa610 and 15xe2x89xa6d xe2x89xa655, each in atomic %.
The use of a thin magnetic film having such a constitution or such compounding ratios makes it possible to increase the specific resistance of the thin magnetic film itself, reduces the loss in the high frequency region and decreases the limitations in the high frequency region which the conventional material has.